1. Field of the Invention
This invention relates to a mold for shaping a skin sheet made of thermoplastic resin such that the skin sheet is heated and softened and thereafter is drawn onto the shaping surfaces of the mold by vacuum, and relates to a method of shaping the same.
2. Description of the Prior Art
A conventional mold for shaping a skin sheet is known as shown in FIGS. 4 and 5.
FIG. 4 is a perspective view of a conventional skin-shaping mold, and FIG. 5 is a descriptive drawing showing a state in which the skin shaped by the skin shaping mold is set in a foaming mold while a foaming process is continuing.
As shown in FIG. 4, the mold 2 comprises a shaping surface 2a and a base surface 2e which are united with each other by means of wood screws, an adhesive agent, and the like.
The mold 2 also has edge line portions 2b at which adjoining side-surfaces intersect. During the skin shaping, an excess skin on the adjoining side surfaces gathers and layers at the edge line portion 2b. However, it is difficult to always obtain a desired molding because different shapes are given to the skin sheet at the edge line portion 2b whenever shaping is performed.
Therefore, the mold 2 is provided with guidance plates 3 of a substantially triangular shape. The triangular guidance plate 3, one side of which is the edge line 2b, is fixed into the base surface 2e in a predetermined direction.
As a result, an excess skin on the adjoining side surfaces is guided to the guidance plate 3 to intentionally form a gathering 6 (in general, called bridge) into which the excess skin is absorbed.
As shown in FIG. 4, a molding (i.e., shaped skin) 4 is obtained by this mold 2 provided with the guidance plates 3 through the following steps. A skin sheet 1 is first heated and softened, and then is moved down toward the mold 2 and is pushed against the mold 2. At the same time, air is drawn out in a moment through small holes 2f formed in the mold 2, and thus the skin sheet 1 is sucked and stuck onto the shaping surface 2a. A surplus of the skin sheet 1 is absorbed into the guidance plate 3, and is formed as the bridge 6. This shaped skin 4 is cooled while keeping its shape, and is stripped from the mold 2 to obtain a finished molding.
After that, foaming is performed using the shaped skin 4 provided with the bridges 6. As shown in FIG. 5, a hollow portion 7a into which the bridge 6 can be inserted is formed in a cavity mold 7. With the bridge 6 inserted in the hollow portion 7a, the shaped skin 4 is pushed and spread to be set on the inner surface of the cavity mold 7.
Thereafter, a predetermined quantity of foaming material 13 is poured into the cavity mold 7 through a mixing head 11 which has been moved over the cavity mold 7, and then a core mold 8 is moved down in a direction of arrow P to create a closing state together with the cavity mold 7.
In a closed foaming mold 12, the foaming material 13 produces a chemical reaction, and cellularly foams and expands. As a result, the foaming mold 12 is filled with the foaming material 13, and thereby a core material 9 and the shaped skin 4 are caused to adhere to each other to form an integral product.
However, the bridge 6 of the shaped skin 4 is still left without changing the form of the bridge 6 which has been given by the guidance plate 3 during the skin shaping, and is inserted in the hollow portion 7a of the cavity mold 7. If foaming is performed using the shaped skin or with the thus formed bridge 6, the foaming material 13 flows into a gap in the bridge 6 because of foaming pressure, and leaks out of the product.
For this reason, there is a fear that a shortage in quantity of the foaming material 13 will be caused and make a thin appearance of the product, or foamed cells will not become uniform because the internal pressure of the foaming mold 12 does not increase. Accordingly, the elasticity of the foaming material 13 will not become uniform either. These make it impossible to stably produce a product superior in quality.
In order to solve this problem, when the aped skin 4 is set in the cavity mold 7, a seal tape 5 is stuck on the gap in the bridge 6 so as to prevent the foaming material 13 from flowing into the gap and leaking out of the product.
Therefore, the seal tape 5 and tape sticking operations are required to prevent the disadvantage. This causes an increase in production costs.